Activated sludge treatment method, and method for upgrading existing waste water treatment equipment using said method

ABSTRACT

The object is to provide an activated sludge treatment method whereby production of excess sludge is brought substantially to zero; and a method for upgrading existing waste water treatment equipment, employing this method. The method includes a step ( 1 ) in which sludge ( 2 ) produced in a sedimentation tank is supplied to a waste water aeration-conditioning tank for activated sludge treatment; a step ( 2 ) in which waste water into which the sludge ( 2 ) has been mixed is subjected to aeration-conditioning to bring the oxidation-reduction potential to a positive value, and supplied to a pressurized flotation concentration-separation tank; a step ( 3 ) in which the sludge ( 1 ) produced through treatment in the pressurized flotation concentration-separation tank is supplied to the bioreactor; a step ( 4 ) in which the treated waste water ( 1 ) separated from the pressurized flotation concentration-separation tank is supplied to a dilute activated sludge aeration tank; a step ( 5 ) in which released water and the sludge ( 3 ) produced by treatment in the bioreactor are supplied to the dilute activated sludge aeration tank; and a step ( 6 ) in which the treated waste water ( 2 ) separated from the dilute activated sludge aeration tank is supplied to the sedimentation tank.

TECHNICAL FIELD

The present invention relates to an activated sludge treatment method,and to a method for upgrading existing waste water treatment equipmentusing this activated sludge treatment method.

TECHNICAL BACKGROUND

The activated sludge treatment method is a very exceptional waste watertreatment method, and is accordingly widely used for waste watertreatment. Various treatment systems adapted to different types of wastewater have been proposed.

In conventional activated sludge treatment methods, utilizing thenatural food chain, various microbes, from soil bacteria to largeprotozoa, are utilized.

An example of an existing activated sludge treatment method is shown inFIG. 4.

Waste water is introduced into a waste water conditioning tank, andsubjected to pre-treatment as needed, eliminating coarse to fine matterdispersed in the waste water, in a pressurized flotation tank. In thecase of effluent having a high oil content, separation-flocculationusing a flocculant is performed by way of a primary treatment. Forexample, inorganic flocculants such as aluminum sulfate (known as“aluminum sulfate, anhydrous”) or polyaluminum chloride (known as“PAC”), or organic flocculants such as polyacrylamide based polymers orthe like, are added to effluent to break down the emulsified state andseparate the oil component and the water component. However, in suchcases, a large amount of flocculant, in the form of sludge, isgenerated. During treatment in the pressurized flotation tank,contaminant substances contained in the waste water are removed throughadhesion to the inorganic flocculant, forming floating scum andgenerating sludge. The sludge is collected in a waste water holdingtank.

Soluble organic matter suited to microorganism treatment is fed as wastewater for treatment to an aeration tank, and after aeration treatmentwith activated sludge, the waste water for treatment is separated fromthe activated sludge and released, while the separated concentratedactive sludge is collected in a sludge holding tank, a portion thereofbeing recirculated to the aeration tank for use as return sludge.

The sludge collected in the sludge holding tank is fed to a dewateringapparatus and transformed into a dewatered cake, which is buried inlandfill, or disposed of as bacterial fertilizer or throughincineration.

Such activated sludge treatment methods have problems such as thefollowing, which need to be solved.

(1) In the case of waste water containing high levels of proteins,modified proteins, cellulose-starch, fats and oils, and other suchpersistent substances, large amounts of dewatered cake which emits afoul odor are generated as excess sludge. To reduce the amount of excesssludge, there has been proposed a method of increasing the size of theaeration tanks and digesting for a prolonged aeration time (lagoonsystem, oxidation ditch). However, with this method, in cases of largeloads imposed by copious amounts of waste water, an extremely largeaeration tank is required, and therefore problems such as lack of a siteor high construction costs may arise. Also, once bulking or a treatmentanomaly has occurred, considerable expense and several days may beneeded for recovery, and consistency of operations at the plant may be aproblem.

(2) When performing microorganism treatments, it is necessary to bringthe inflowing waste water to neutral pH. However, when chemicals areadded to neutralize, in addition to outlays for the chemicals,accelerated corrosion of equipment can become a problem. Another problemis that the pH of the released treated water varies greatly when thehydrogen ion concentration (hereinafter termed pH) of inflowing wastewater is regulated.

(3) With activated sludge methods, inflow of toxic substances that couldrender the activated sludge sterile will damage the activated sludge,which tends to give rise to a loss of waste water purifying function, orto filamentous bulking. However, as it is not possible to completelyavoid the presence in waste water of low levels of bactericides orsubstances having adverse effects on activated sludge, elimination ofsuch harmful substances is a problem.

(4) In activated sludge treatment plants in which large volumes oforganic contaminant substances are treated, the following problem mayoccur. The inflow of water decreases greatly at night and on non-workingdays. In cases of numerous consecutive non-working days, the goodactivated sludge microbes are not supplied with a constant amount ofcontaminant substances, and are reduced in number due to excessiveaeration. Further, the sludge breaks up due to the excess load. As aresult, stable growth of activated sludge microbes cannot be assured,and bulking or sludge flotation may arise, which tends to reduce thetreatment power of the activated sludge. Particularly in cases in whichthere are large fluctuations in contaminant substance component levelsin inflowing waste water for treatment, or in cases in which the loadincreases sharply due to consecutive non-working days, bulking is proneto occur. To prevent this, larger waste water conditioning tanks may beconstructed, storing large quantities of waste water in the hopes ofachieving uniform quality of the waste water, which is then continuouslysupplied at a constant supply rate to the aeration tank; however,problems relating to restrictions of the size of the area of the siteand construction costs may be encountered.

(5) The high-speed aeration activated sludge treatment method is ahighly efficient waste water treatment method requiring a minimalinstallation area. However, as the process is a completely mixed systemin which the activated sludge and the waste water are constantly presenttogether, the problem of bulking due to filamentous bacteria tends toarise. Moreover, as sewage treatment facilities, such systems aretypically classed as secondary treatment facilities, and in recent yearsfacilities that are incapable of adequate treatment have largelydisappeared.

In order to solve the above described problems, the inventors previouslydeveloped a bioreactor and a waste water treatment method (see PatentDocument 1), and achieved good results in waste water treatment innumerous fields.

Moreover, as one method for reducing excess sludge, there has beendisclosed a method involving returning excess sludge to the aerationtank after ozone treatment (Non-patent Document 1). Other known methodsinvolve treatment with thermophiles, mechanical crushing, or chemicaltreatment, followed by return to the aeration tank.

However, as waste water treatments become increasingly diverse,regulations with respect to the environmental load become morestringent, and in some cases it proves difficult to minimize excesssludge, despite performing waste water treatment by the various methodsmentioned above.

Another problem is that with existing waste water treatment facilitiesemploying conventional methods, the waste water treatment equipmentinstallation sites are quite large in area, making activated sludgetreatment insufficient, whereby large amounts of excess sludge aregenerated.

PRIOR ART DOCUMENT Non-Patent Document

-   Non-patent Document 1: YASUI, Hidenari, Kagaku Kogaku, Vol. 66, No.    6, pp. 329-331, 2002

Patent Document

-   Patent Document 1: Japanese Patent Publication No. 4142138

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The present invention was devised in order to solve the above mentionedproblems, and has as an object to provide a waste water treatment methodemploying an activated sludge treatment method, wherein the activatedsludge treatment method reduces production of excess sludgesubstantially to zero; as well as a method for upgrading existing wastewater treatment facilities using this activated sludge treatment method.

Means to Solving the Problem

The activated sludge treatment method of the present invention is anactivated sludge treatment method for treatment of waste water by acirculation system equipped with a waste water aeration-conditioningtank, a pressurized flotation concentration-separation tank, a diluteactivated sludge aeration tank, a bioreactor, and a sedimentation tank,sludge being circulated among the tanks, the method characterized byhaving:

a step 1 in which sludge 2 produced in the sedimentation tank issupplied to the waste water aeration-conditioning tank supplied withwaste water prior to treatment;

a step 2 in which waste water into which the sludge 2 has been mixed issubjected to aeration-conditioning in the waste wateraeration-conditioning tank, to bring the oxidation-reduction potential(hereinafter “ORP”) to a positive value, and the conditioned waste wateris then supplied to the pressurized flotation concentration-separationtank;

a step 3 in which the sludge 1 produced through treatment in thepressurized flotation concentration-separation tank is supplied to thebioreactor;

a step 4 in which the treated waste water 1 separated from thepressurized flotation concentration-separation tank is supplied to thedilute activated sludge aeration tank;

a step 5 in which released water and the sludge 3 produced by treatmentin the bioreactor are supplied to the dilute activated sludge aerationtank; and

a step 6 in which the treated waste water 2 separated from the diluteactivated sludge aeration tank is supplied to the sedimentation tank.

The method is further characterized in that the sludge 2 supplied to thewaste water aeration-conditioning tank is supplied in a range such thatthe sludge concentration within the waste water aeration-conditioningtank, expressed as the mixed liquor suspended solids (hereinafter“MLSS”) is 500-8,000 mg/L.

The bioreactor employed in the activated sludge treatment method of thepresent invention is equipped with an outer tank, a cylindrical innertank situated in the interior of the outer tank and having openings attop and bottom, a circulation rate control device provided in an upperpart of the cylindrical inner tank, and adapted for controlling the rateof circulation of treated water inside the tank, a cylindrical controlplate provided to the outside perimeter in an upper part of thecylindrical inner tank, and adapted for inducing sedimentation of thesludge, treated water quality measurement devices provided outside andinside of the cylindrical inner tank, a waste water supply port providedto a circulation pathway of the treated water circulated within theouter tank and the inner tank, and a treated water release port providedto an upper part of the outer tank.

The cylindrical inner tank constituting the bioreactor is divided, by apartitioning wall having a passage hole in a center part, into acylindrical top part and a cylindrical bottom part, with the cylindricaltop part constituting an aerobic microorganism treatment tank having anopened conical trapezoidal-shaped part at the top face and the bottomface and provided with a plurality of air injection ports in aperipheral edge part of the partitioning wall and surrounding thepassage hole within the cylindrical top part, and the cylindrical bottompart constituting an anaerobic microorganism treatment tank having anopen part at the bottom face, and is provided with stirring devices forrespectively stirring the aerobic microorganism treatment tank and theanaerobic microorganism treatment tank.

The bioreactor is provided with means for detecting at least onemeasured value, selected from the pH, the oxidation-reduction potential(hereinafter “ORP”), and the dissolved oxygen (hereinafter “DO”) contentof the treated water measured by the treated water quality measurementdevices, and with means provided to the circulation rate control deviceaccording to the detected measured value, and adapted for controllingthe rate at which water circulates within the tank to 3-20, throughcontrol of at least one quantity selected from opening-closing of afluid level adjustment valve, vertical movement of a fluid leveladjustment control panel, and the quantity of air blown in from the airinjection ports. Herein, the circulation rate of treated water withinthe reaction tank is a quantity defined by the following expression.Treated water circulation rate=quantity of treated water discharged frominner tank upper part (m³/day)/waste water supply quantity (m³/day)

The method is further characterized in that in the bioreactor, anaerobicmicroorganism treatment and aerobic microorganism treatment take placein successive fashion through circulation of activated sludge, togetherwith waste water supplied from the waste water supply port, within thetank, through the interior of the cylindrical inner tank, the outsideperipheral face of the cylindrical inner tank, and within activatedsludge that has sedimented to a bottom part of the outer tank.

In particular, the method is characterized in that the waste watersupply port is constituted by a plurality of discharge ports or slitsprovided to a ring-shaped waste water supply part situated in a bottompart of the opening part of the anaerobic microorganism treatment tank.The method is further characterized in that the cylindrical bottom parthas a capacity that is 1/10 to 1-fold the capacity of the cylindricaltop part.

The method for upgrading existing waste water treatment according to thepresent invention is an upgrading method for reducing sludge produced bywaste water treatment equipment, to a lower level than sludge producedby the existing waste water treatment equipment, wherein the upgradingmethod is characterized by including a step in which the above describedbioreactor 3 is newly equipped with an existing or upgraded pressurizedflotation concentration-separation tank and dilute activated sludgeaeration tank, and a circulation step in which sludge is circulatedaccording to the above described activated sludge treatment method ofthe present invention, via the newly installed bioreactor.

Effect of the Invention

The method of the present invention provides an activated sludgetreatment method whereby sludge produced respectively in a pressurizedflotation concentration-separation tank, activated sludge aeration tank,and bioreactor employed as waste water treatment equipment, iscirculated among the tanks by the method according to claim 1, while aportion of the sludge produced by the activated sludge aeration tank issupplied to the waste water aeration-conditioning tank for waste waterundergoing activated sludge treatment, whereby substantially no excesssludge is discharged.

By newly providing the bioreactor according to claim 3, it is possiblefor upgraded existing waste water treatment equipment to carry out wastewater treatment with substantially no discharge of excess sludge.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of an activated sludge treatment method;

FIG. 2 is a cross sectional view of a bioreactor;

FIG. 3 is a diagram showing a circulation pathway of treated water andactivated sludge in a bioreactor; and

FIG. 4 is a block diagram of an existing activated sludge treatmentmethod.

MODE FOR CARRYING OUT THE INVENTION

A block diagram of an activated sludge treatment method of the presentinvention is shown in FIG. 1.

Sludge 1, sludge 2, and sludge 3 which are produced respectively in apressurized flotation concentration-separation tank, a dilute activatedsludge aeration tank, a bioreactor, and a sedimentation tank arecirculated over a pathway shown respectively by steps 1 to 5. In thecourse of being circulated, the sludge is digested, and substantially noexcess sludge is discharged. The steps are described in order below.

Step 1:

Step 1 is a step in which the sludge 2 produced by the sedimentationtank is supplied to the waste water aeration-conditioning tank for thewaste water which is undergoing activated sludge treatment.

In the case of upgrading existing waste water treatment equipment, thewaste water aeration-conditioning tank is obtained by retrofitting theexisting waste water tank with air injection equipment.

Large solids present in treated waste water are removed by a screen orthe like, and the treated waste water is collected in the waste wateraeration-conditioning tank. This waste water aeration-conditioning tankis supplied with the sludge 2 produced in the sedimentation tank, whichis mixed with the waste water through agitation, whereupon persistentsubstances, toxic substances that could break down the activated sludge,and other such contaminant substances in waste water that could giverise to anomalies in activated sludge treatment are adsorbed throughcontact with the sludge 2. Because this sludge 2 is has been treated inthe dilute activated sludge aeration tank and passed through thesedimentation tank, the sludge contains activated sludge microbes suitedto the waste water being treated. Therefore, by supplying the sludge 2to the waste water, damage to the activated sludge in the diluteactivated sludge aeration tank is prevented, and the sludge can bemaintained in a state of high activity, whereby the occurrence ofanomalous phenomena during treatment due to bulking of the diluteactivated sludge or to foaming scum can be reduced, making treatmentmore consistent.

The sludge 2 supplied to the waste water aeration-conditioning tank issupplied at a sludge concentration, expressed as MLSS in the waste wateraeration-conditioning tank, within a range of 500-8,000 mg/L, andpreferably supplied within a range of 1,000-5,000 mg/L. When the MLSS isless than 500 mg/L, contaminant substances having adverse effects on theactivated sludge cannot be adsorbed by the sludge 2, and thereforeactivated sludge treatment becomes inconsistent. When the MLSS exceeds8,000 mg/L, the sludge 2 adsorbs substantially all contaminantsubstances, reducing the biological oxygen demand (hereinafter “BOD”)contained in the treated waste water.

Step 2:

Step 2 is a step in which the waste water into which the sludge 2 hasbeen mixed undergoes aeration-conditioning in the waste wateraeration-conditioning tank, to bring the ORP of the waste water to apositive value, and the waste water is then supplied to the pressurizedflotation concentration-separation tank. Through aeration-conditioningto a positive value, activated sludge treatment to oxidize hydrogensulfide, ammonia, mercaptans, and other compounds that cause foul odors,substantially eliminating odors, can be accomplished.

Aeration treatment in the waste water aeration-conditioning tankinvolves aeration treatment for a waste water residence time of 3 hoursor more, and preferably 5 hours or more. The waste water havingundergone aeration treatment in the presence of the sludge 2 andcontaining sludge is then supplied to the pressurized flotationconcentration-separation tank.

Step 3:

Step 3 is a step in which the sludge 1 produced through treatment in thepressurized flotation concentration-separation tank is supplied to thebioreactor. Here, the sludge 1 is not dry sludge, but liquid sludgecontaining water.

As the waste water supplied to the pressurized flotationconcentration-separation tank has undergone aeration treatment in thewaste water aeration-conditioning tank, the pH has been regulated in anatural manner due to the pH buffering action of the microbes, thereforeobviating the need for chemicals and equipment to neutralize acids orbases. For this reason, not only can the site be used effectively, buttreatment can be accomplished without chemical dosing, thereby saving onchemical costs.

Even when toxic substances, such as bactericides or the like, that canbreak down activated sludge when adsorbed by activated sludge arepresent in the waste water, these are adsorbed beforehand by the sludge2, and are removed from the system as the sludge 1 through pressurizedflotation, and therefore have no adverse effects on the activated sludgein the dilute activated sludge aeration tank, whereby activated sludgetreatment can be carried out in a consistent manner even when the wastewater contains admixed bactericides.

Step 4:

Step 4 is a step in which the treated waste water 1 separated from thepressurized flotation concentration-separation tank is supplied to thedilute activated sludge aeration tank for treatment.

As the dilute activated sludge aeration tank, an aerobic activatedsludge treatment tank employed in existing activated sludge treatmentmethods can be utilized without modification.

The dilute activated sludge aeration tank is supplied with the treatedwaste water 1, and with the sludge 3 produced in the bioreactor, shownin Step 5. This sludge 3 is digested sludge which has been digestedthrough aeration with oxygen-containing gas for 1 to 7 days in thedilute activated sludge aeration tank.

Step 5:

Step 5 is a step in which the sludge 3 produced through treatment in thebioreactor is supplied to the above mentioned dilute activated sludgeaeration tank.

In the present invention, anaerobic treatment refers to treatmentconducted in a state in which the DO is less than 0.05 mg/L, and aerobictreatment to treatment conducted in a state in which the DO is 0.05 mg/Lor above, preferably 0.1 mg/L or above, and more preferably 0.2 mg/L orabove. It further refers to operations involving treatment in which theORP during anaerobic treatment is less than −80 mV, and the ORP duringaerobic treatment is −80 mV or above, and preferably positive.

In the bioreactor, the sludge 1 is digested anaerobically andaerobically, whereby substantially all of the contaminant substancesadsorbed by the sludge 1 are decomposed and converted to carbon dioxidegas, water, or gases such as nitrogen gas, methane gas, and the like.Additionally, the sludge 1 is used for microorganism growth, becomingdigested sludge having substantially undergone conversion to microbes,thereby greatly reducing the amount of sludge. Even when very minimalamounts of sludge have been produced, the flocculating and dewateringproperties of the sludge are good, and the amount of dewatered cakeproduced can be greatly reduced, due to the reduced water content of thedewatered cake.

The dewatered cake obtained thereby is a dewatered cake of the sludge 3which is obtained in mature microbe form, whereby the dewatered cake haslow water content and reduced emission of foul odors, and can bedisposed of in landfills, which involve low sludge treatment costs.

The bioreactor can be constituted by two tanks, an anaerobic bioreactorfor the concentrated sludge, and an aerobic bioreactor, for example, oneof larger internal capacity than the anaerobic bioreactor.

Here, the anaerobic bioreactor may be any tank in which activated sludgecan be treated under anaerobic conditions. The aerobic bioreactor is anactivated sludge treatment tank generally identical to the abovedescribed activated sludge aeration tank, and may be supplied with gascontaining oxygen, as needed.

The amount in which the sludge 3 produced in the aerobic bioreactor issupplied to the dilute activated sludge aeration tank is an amountderived on a concentration conversion basis, such that the amount of drysludge solids contained in the sludge 3 is substantially equal to theamount of dry solids of the reacted sludge contained in the diluteactivated sludge aeration tank, maintaining the amount of sludge in thedilute activated sludge aeration tank at a constant level. To cite oneexample, in a case in which reacted sludge of 6,000 mg/L concentrationcontained in the dilute activated sludge aeration tank has been suppliedat a rate of 1 m³/hour, the sludge 3 of 22,000 mg/L concentration wouldbe supplied at a rate of 0.27 m³/hour. However, in cases in which theamount of water entering the dilute activated sludge aeration tank issmall, the sludge 3 would be supplied in an amount 20-200% of normal.

The bioreactor is shown in FIG. 2. FIG. 2 is a cross sectional view ofthe bioreactor.

The bioreactor 1 is constituted by an outer tank 2, a cylindrical innertank 3 situated in the interior of the outer tank 2, a circulation ratecontrol device 4 provided in an upper part of the cylindrical inner tank3, a cylindrical control plate 5 provided to the outside perimeter ofthe cylindrical inner tank 3, treated water quality measurement devices6, and a sludge extraction port 13.

The outer tank 2 has an external appearance of circular cylindricalform, including a base panel 2 a constituting the bottom face, acylindrical side face 2 b, and an upper face part 2 c. The center of thecylinder is provided with a rotating shaft 7 for attachment of anagitator paddle or the like. This rotating shaft 7 is rotatably securedby a cradle 2 d provided at the center of the base panel 2 a, and abearing 2 e provided at the center of the upper face part 2 c. Therotating shaft 7 is rotated by a drive device 2 f. The upper face part 2c rotatably fastens the rotating shaft 7, as well as retaining thecylindrical inner tank 3 by retainers or the like.

The bottom part of the outer tank 2 is provided with a waste watersupply port 10. The waste water supply port 10 is constituted by aplurality of discharge ports 10 b or slits provided to a ring-shapedwaste water supply part 10 a situated below a lower opening part 3 f ofthe cylindrical inner tank 3. With the waste water supply port 10arranged in this way, the anaerobic sludge may be sufficiently stirred.The waste water supply port 10 may be provided at another location onthe circulation pathway for the treated water, other than the lower partof the cylindrical inner tank 3.

A treated water release port 11 for the purified water is provided inthe upper part of the outer tank 2, and a sedimentation-solidificationprevention device 12 for preventing sedimentation-solidification ofsedimented sludge is provided to an inside face of the outer tank.

As examples of the sedimentation-solidification preventing device, theremay be cited: (1) a vibrating device provided to the inner wall or outerwall of a bottom part of the outer tank in which sludge sedimentes; (2)a device having a vibrating plate provided near the inner wall, and avibration generator provided to an upper part of the outer tank, fortransmitting vibration to the vibrating plate; (3) a scraper provided tothe inner wall of a bottom part of the outer tank in which sludgesedimentes; (4) an stirring flow producing device for producing asludge-stirring flow along the inner wall of a bottom part of the outertank, in particular, a moveable fluid jet nozzle for jetting a fluidwhile moving along a sloped face of the inner wall, or jet nozzlessecured at prescribed intervals to a sloped surface of the inner wall;or (5) a pump for suctioning sludge that has sedimented into a bottompart of the outer tank, and expelling it into the anaerobicmicroorganism treatment tank, while the stirring flow producing devicemoves across the bottom face or sloped face of the inner wall, or pumpssecured at prescribed intervals to the bottom face or sloped face of theinner wall, for suctioning sludge that has sedimented into a bottom partof the outer tank, and expelling it into the anaerobic microorganismtreatment tank; or the like.

The cylindrical inner tank 3 is situated within the outer tank providedwith the above described sedimentation-solidification prevention device12.

The cylindrical inner tank 3, the lateral cross section of which isapproximately circular, is divided by a partitioning wall 3 a into acylindrical top part 3 c and a cylindrical bottom part 3 d. A passagehole 3 b through which the cylindrical top part 3 c and the cylindricalbottom part 3 d communicate is formed in the center of the partitioningwall 3 a.

Due to the presence of the partitioning wall 3 a, even in cases in whichthe bioreactor has a large capacity, the cylindrical top part 3 c andthe cylindrical bottom part 3 d are sufficiently separated, andactivated sludge treatment can be performed within the respective tanks.An aerobic microorganism treatment reaction can be performedsufficiently within the cylindrical top part 3 c, and an anaerobicmicroorganism treatment reaction can be performed sufficiently withinthe cylindrical bottom part 3 d, respectively. In cases in which thepartitioning wall 3 a has a large surface area, it is reinforced by asupport member 3 g or the like.

The passage hole 3 b has a diameter of a size such that activated sludgehaving undergone anaerobic microorganism treatment can move from thecylindrical bottom part 3 d into the cylindrical top part 3 c which isthe aerobic microorganism treatment tank. The diameter of the passagehole 3 b will be regulated according to factors such as the capacity ofthe bioreactor, the quality and amount of waste water being treated, andthe like.

The cylindrical top part 3 c has a opened conical trapezoidal-shapedpart at the top and bottom faces. That is, the shape is one in which thedistal end of the cylindrical part constricts in diameter at apredetermined angle in the height direction. The slope angle of a crosssection in the height direction passing through the center of theconical trapezoidal shape is from 40 to 60 degrees, and preferably 45degrees. By adopting a slope angle within this range, sludge containedin treated water discharged from the upper part of the aerobic tankflocculates readily by flowing down along the outer face of the conicaltrapezoidal shape, making rapid forced sedimentation possible. Due toflocculation of the sludge, the sludge and the purified treated waterare readily separated.

The cylindrical top part 3 c is an aerobic microorganism treatment tankprovided in the interior with air injection ports 8 and 8 a. The airinjection ports 8 are provided around the center shaft 7, andsurrounding the passage hole 3 b, and can be secured onto thepartitioning wall 3 a by support posts or the like, not illustrated. Theair jet holes of the air injection ports 8 are preferably situatedfacing downward, so as to be able to contribute to agitation of thetreated water and sludge within the aerobic tank.

The air injection ports 8 a can be constituted by a plurality of airholes 8 c provided to an air injection part 8 b, the air injection part8 b being ring-shaped in plan view and situated in a peripheral edgepart of the partitioning wall inside the cylindrical top part 3 c, or byslits formed in the upper face or side face of the air injection part 8b.

The circulated amount of treated water can be varied within a range of3-20 without the use of a circulating pump, by controlling the amount ofair injected from the air injection ports 8 and 8 a and the controlquantity of the circulation rate control device, discussed below. In sodoing, aerobic microorganism treatment under appropriate nitrificationconditions, and anaerobic microorganism treatment under appropriatedenitrification conditions, can be easily established. Further,solid-liquid separation of sludge through the principle of forciblesedimentation at the outside peripheral face of the aerobicmicroorganism treatment tank having the above mentioned slope angleproceeds in extremely efficient fashion, whereby the aerobic andanaerobic microorganism treatment reactions can be performed efficientlywithin the same tank of upright design.

Additionally, an alkali supply port or a supply for acid, omitted fromthe illustration, can be provided within the aerobic tank.

The cylindrical bottom part 3 d is an anaerobic microorganism treatmenttank having a capacity, for example, that is 1/10 to 1-fold the capacityof the cylindrical top part. When the capacity is within this range,aerobic microorganism treatment reactions and anaerobic microorganismtreatment reactions of waste water containing, for example, contaminantsubstances that contain high concentrations of nitrogen, can beperformed efficiently. The interior of the anaerobic microorganismtreatment tank can be provided with a denitrifying microbe nutrientsupply port, omitted from the illustration.

In cases in which there are few hydrogen donors in the waste water, anddenitrification of the nitrogen in nitrates is carried out by supplyinghydrogen donors such as methanol, acetic acid, or the like, it ispreferable for the capacity of the anaerobic microorganism treatmenttank to be larger than that of the aerobic microorganism treatment tank.

The shape of the cylindrical bottom part 3 d is a shape having in thecylindrical bottom part thereof an inverted conical trapezoidal shapehaving an opening 3 f larger in area than the opening 3 e of thecylindrical top part 3 c. That is, the shape is one in which the distalend of the cylindrical part constricts in diameter at a prescribed anglein the direction of the lower part. By adopting a large area for theopening 3 f, the sludge inside the anaerobic microorganism treatmenttank can be readily stirred.

In cases in which the above described inverted conical trapezoidal shapeis adopted as the shape of the cylindrical bottom part 3 d, it ispreferable to adopt the same angle as the above described prescribedangle for the inner face 2 g of the lower part of the outer tank 2, assedimentation-solidification of sludge can be prevented by doing so.

The cylindrical inner tank 3 is provided with an agitator device for thepurpose of bringing about sufficient treatment reaction of the treatedwater and the activated sludge in the cylindrical top part 3 c, whichconstitutes the aerobic microorganism treatment tank, and thecylindrical bottom part 3 d, which constitutes the anaerobicmicroorganism treatment tank.

The agitator device is preferably constituted by agitator paddles 7 a, 7b secured to the rotating shaft 7 which has been attached at the centerof the cylindrical inner tank 3. The agitator paddle 7 a is preferably aturbine paddle provided inside the cylindrical top part 3 c, and adaptedto bring about sufficient aerobic microorganism treatment reaction.Apart from a turbine paddle, an agitator of any shape can be used,provided that mixing of air and water can take place at a relatively lowrotation speed such that there is no appreciable decline in the aerationcapability, according to the air injection amount.

The agitator paddle 7 b is a propeller paddle provided inside thecylindrical bottom part 3 d, and able to bring about a sufficientanaerobic microorganism treatment reaction.

The partitioning wall 3 a provided within the cylindrical inner tank 3is supported by a support post 9 secured rising up from the base panel 2a which constitutes the bottom face of the outer tank 2.

The cylindrical inner tank 3 is retained within the outer tank throughthe support provided by this support post 9, and through supports whichbridge the upper part of the outer tank 2.

The circulation rate control device 4 for controlling the rate ofcirculation of treated water inside the reaction tank is provided in theupper part of the cylindrical inner tank 3. Control of the rate ofcirculation of treated water inside the reaction tank by the circulationrate control device 4 is specifically accomplished through opening andclosing of a fluid level regulator valve, or up and down movement of afluid level regulator plate, or the like. When the fluid level regulatorvalve is fully open, or when the level regulator plate is at the lowestposition, the water level of the treated water reaches its lowest level.This water level is denoted by “A.”

Control of the circulation rate within the reaction tank can also beaccomplished through control of the amount of air injected by the airinjection port 8 and/or 8 a. The circulation rate increases as greateramounts of air are injected. A combination of opening and closing of thefluid level regulator valve and regulation of the amount of airinjection can be employed as well.

In association with larger scale of the anaerobic microorganismtreatment tank and the anaerobic microorganism treatment tank, theaeration air alone may no longer suffice to maintain the necessarycirculation flow rate of the sludge, and in some instances adverseeffects may be produced by injection of excess air. In anticipation ofsuch cases, it is necessary to provide the air injection ports denotedby 8 a in FIG. 2. The advantage is that the regulation of the airinjection amount and ORP is dramatically easier, due to the airinjection ports 8 a which have poor aeration efficiency. The airinjection ports 8 a are constituted, for example, by installing the airinjection part 8 b of ring shape in plan view, centered on the agitatorpaddle 7 a in the aerobic section at the upper face of the partitioningwall 3 a and communicating with an external blower or the like, andproviding the air injection part 8 b with holes or slits. This not onlyincreases the amount of air injection; a baffle effect arises on thepart of the agitator paddle 7 a as well, giving rise to a synergisticeffect through efficient agitation.

Through opening and closing of a fluid level regulator valve and/orregulation of the amount of air injection, the circulation rate of thetreated water can be varied without the use of a pump. As discussedbelow, denitrification, dephosphorization, and the like are accomplishedby circulating the treated water from the aerobic microorganismtreatment tank 3 c past the cylindrical control plate 5 situated outsidethis tank and into the anaerobic microorganism treatment tank 3 d, andthen from the anaerobic microorganism treatment tank 3 d into theaerobic microorganism treatment tank 3 c. Consequently, through controlof the treated water circulation rate on the basis of a prescribedcontrol program in response to detected values, denitrification,dephosphorization, and the like can take place in optimal fashion.

The cylindrical control plate 5 is situated at the outside periphery ofthe upper part of the cylindrical inner tank 3. The cylindrical controlplate 5 is constituted by a cylinder which is open at the top face andthe bottom face, the bottom face 5 a of the cylindrical control plate 5being situated in proximity to the sloped face of the cylindrical innertank 3. In the sloped face section situated in proximity thereto, thereis formed a sludge sedimentation part where sludge concentration takesplace, together with separation of treated water. This proximalsituation of the bottom face 5 a also makes possible rapid forciblesedimentation of sludge. In preferred practice, the distance of thebottom face 5 a with respect to the sloped face of the cylindrical innertank 3 can be adjusted. The shape of the cylindrical control plate 5 maybe a vertical cylindrical shape in which the open faces at the top faceand the bottom face have identical area, or an inverted conicaltrapezoidal shape in which the opening area of the top face is largerthan the opening area of the bottom face.

The treated water quality measurement devices 6 are provided inside andoutside the cylindrical inner tank 2, within the bioreactor. The treatedwater quality measurement devices 6 are devices for measuring the pH,ORP, and DO of the treated water.

The treated water circulation rate within bioreactor is 3-20, andpreferably 5-20. When the treated water circulation rate is less than 3,the aerobic microorganism treatment reaction proceeds more readily,whereas in excess of 20, the balance between the aerobic microorganismtreatment reaction and the anaerobic microorganism treatment reaction islost, and denitrification and dephosphorization of the waste water canno longer take place. That is, by setting the treated water circulationrate to within this range, the ORP of the treated water as measured bythe treated water quality measurement devices can be maintained at −10mV or less, preferably −50 mV or less, in the anaerobic microorganismtreatment tank, and at +10 mV or above, preferably +100 mV or above, inthe aerobic microorganism treatment tank. As a result, the aerobicmicroorganism treatment reaction and the anaerobic microorganismtreatment reaction take place sufficiently, with denitrification anddephosphorization taking place in successive fashion. Under theseconditions, the pH in the aerobic microorganism treatment reaction tankis within the range 4.5-8.5, and preferably 5.5-7.5.

The wastewater treatment method employing the bioreactor 1 has thefollowing exceptional features, as compared with conventional wastewater treatment methods.

The conventional waste water treatment methods are methods in whichwaste water and return sludge are mixed in constant proportions andflowed into an aeration tank, the return sludge in contact therewith atthat time and the waste water being pushed to flow until the treatedwater and the sludge are separated in the sedimentation tankconstituting the next step.

The waste water treatment method employing the bioreactor 1 is a methodin which a circulating flow of vertically circulating activated sludgeis formed, and the waste water is added into this circulating flow. Nocirculating pump is used to create the circulating flow of activatedsludge; rather, a rising flow produced by the aeration air used formicroorganism treatment is utilized to form the circulating flow ofsludge, thereby providing an energy-saving waste water treatment method.Furthermore, the treatment method is one in which aeration in theaerobic microorganism treatment tank is carried out efficiently.

The location for addition of the waste water may be any point on thepathway of the circulating flow, preferably the aerobic microorganismtreatment tank. The anaerobic microorganism treatment tank is still morepreferable. In the case of treatment employing a circulating flow in thewastewater treatment method of the present invention, even for wastewater having a BOD of at least 800 mg/L and total nitrogen (hereinafter“T-N”) of 40 mg/L or above, the BOD of the treated water is typicallyvery low (20 mg/L or less), and operation is typically possible at awater quality such that the BOD of the released water is 10 mg/L orless.

When waste water is added to the sludge setting section on thecirculating flow pathway formed at the outside peripheral face of thecylindrical inner tank constituting the aerobic microorganism treatmenttank, there will be insufficient contact between the sludge and thewaste water, and in some cases contaminant substances may not besufficiently absorbed. In such cases, there are cases in whichcontaminant substances in a portion of the untreated waste water becomeadmixed into the treated water, with adverse effects on the treatedwater. However, in cases in which standards for water quality are lessstringent, for example, in primary treatment equipment applications,such as sewage line release water or the like having a BOD of 300 mg/Lor less, or of 600 mg/L or less, there are cases in which waste watercan be added to the sludge setting section on the circulating flowpathway.

Circulation of treated water and activated sludge in the bioreactor 1 isdescribed below using FIG. 3. FIG. 3 is a drawing showing thecirculation pathway of treated water and activated sludge in thebioreactor 1. In FIG. 3, hatched sections indicate sections of highactivated sludge concentration, and the arrows represent directions ofcirculation of the treated water and activated sludge.

The bioreactor 1 contains 5,000-12,000 mg/L (solids conversion) ofactivated sludge, and the waste water 1 for treatment is first broughtinto contact under anaerobic conditions with the activated sludge in thecylindrical bottom part 3 d, whereupon a denitrification reaction takesplace. The waste water 1 for treatment supplied by the waste watersupply port 10 and the circulating activated sludge are circulatedwithin the cylindrical bottom part 3 d through rotation of the agitatorpaddle or jetting of air from a diffuser tube, bringing about ananaerobic microorganism treatment reaction.

Next, the waste water and the activated sludge move through the passagehole 3 b into the cylindrical top part 3 c into which air is injected,and while in contact with the activated sludge under aerobic conditions,are circulated within the cylindrical top part 3 c through rotation ofthe agitator paddle or jetting of air from the air injection port,whereupon a nitrification reaction, which is an aerobic microorganismtreatment reaction, proceeds. As the nitrification reaction proceeds,the pH of the treated water drops. The pH value, ORP, and DO of thetreated water are measured by the treated water quality measurementdevices 6, and the circulation amount of the waste water or treatedwater is determined on the basis of these values. Specifically, thetreated water is circulated while regulating the air injection amountand the like so as to maintain the ORP at +10 mV or above in the aerobicreaction treatment tank where the nitrification reaction takes place,and at −10 mV or below in the anaerobic reaction treatment tank wherethe denitrification reaction takes place. Control of the circulationamount can be readily performed without the use of a circulating pump orthe like, through control of the air amount and/or of the circulationrate control device. For this reason, the waste water treatment methodof the present invention represents an energy-saving waste watertreatment method. Of the equipment, including the bioreactor, of thepresent invention, each microorganism reaction unit can be regulated inrespective fashion, with control thereof being programmed in advance,making unmanned automated operation easy, and affording the feature of alabor-saving plant.

With the circulation rate controlled by the circulation rate controldevice 4, a portion of the activated sludge and the treated waterdischarged from the top part of the cylindrical top part 3 c flows downthe conical trapezoidal peripheral face having a 45 degree slope angle.The outflowing activated sludge and the treated water pass through asludge concentration part 5 b formed by the sloped face and thecylindrical control plate 5 situated in proximity to the sloped face ofthe conical trapezoidal peripheral face, thereby making possible rapidforcible sedimentation of the activated sludge. The purified treatedwater and the activated sludge are readily separated, and the separatedtreated water is released through the treated water release port 11.

The activated sludge having undergone rapid forcible sedimentationaccumulates as the activated sludge becomes concentrated between theouter tank inner face and the inner tank outside peripheral face. Thisaccumulated activated sludge, while mixing with the treated water, movesto the anaerobic microorganism treatment reaction part, and circulatesthrough the bioreactor.

According to the waste water treatment method of the present invention,the activated sludge is circulated within the anaerobic and aerobictanks at a circulation rate of 3-20 while being concentrated, wherebyfluctuations in the waste water load can be readily accommodated.Because the circulation rate is maintained in this range, the activatedsludge becomes acclimated, becoming activated sludge that is optimal forwater treatment. Under these conditions, the pH in the aerobic treatmenttank is the range 4.5-8.5, and preferably 5.5-7.5.

In the bioreactors, irrespective of low BOD load of the waste water, incases of high nitrogen concentration, it is preferable to add to theanaerobic reaction process part a denitrification bacteria nutrientcomposed of an organic substance such as a proton donor or the like, forexample methanol. In such cases, as the pH of the treated water tends torise, it is preferable to also add a mineral acid such as hydrochloricacid or the like.

The waste water treatment method of the present invention may employ asingle bioreactor, or a plurality of tanks. In this case, release waterfrom the first tank is introduced into the waste water supply port ofthe second tank. In a case in which, for example, two bioreactors arelinked in series, waste water treatment can be performed moreeffectively by adopting a ratio of the capacity of the nitrificationreaction part and the capacity of the denitrification reaction part inthe second tank that is different from this ratio in the first tank.Specifically, denitrification-dephosphorization can be performed bysetting this capacity ratio to one smaller than that in the first tank.

By situating the bioreactor in the waste water treatment step, (1)anaerobic-aerobic operation can take place while minimizing theproduction of toxic gases, thereby improving the autodigestioncapability of the activated sludge microbes; and (2) microbes capable ofselectively decomposing contaminant substances in waste water as aselective culture tank become acclimated, so that persistent substancescan be readily treated.

Step 6:

Step 6 is a step in which the treated waste water 2 separated from thedilute activated sludge aeration tank is supplied to the sedimentationtank. The sludge contained in the treated waste water 2 sediments in thesedimentation tank, and the clear supernatant is released as releasewater.

The method for upgrading existing waste water treatment equipmentaccording to the present invention is a method for retrofitting existingwater treatment equipment with the above described bioreactor. Byretrofitting the bioreactor and circulating sludge through thebioreactor, the amount of sludge produced by existing water treatmentequipment, particularly that installed at a food production facility,can be brought substantially to zero. Therefore, the need for sludgecollection tanks and dewatering devices, which occupy a major part ofexisting water treatment equipment, is obviated, and the installationarea for the water treatment equipment can be smaller.

EXAMPLES Example 1

Wastewater discharged from a food production facility was treated by themethod shown in FIG. 1.

Prior to treatment, the waste water had a BOD of 800 mg/L, a chemicaloxygen demand (hereinafter “COD”) of 300 mg/L, a T-N of 50 mg/L, anormal hexane-extracted oil component concentration (hereinafter“n-Hex”) of 50 mg/L, and a suspended solids concentration (hereinafter“SS”) of 200 mg/L, the amount of treated water being 1,500 m³/day. Inthe past, the waste water underwent waste water treatment by the methodshown in FIG. 4, producing 150 tons/month of dewatered cake.

The capacity of the waste water aeration-conditioning tank was 1,500 m³,the capacity of the pressurized flotation concentration-separation tankwas 250 m³, the capacity of the dilute activated sludge aeration tankwas 1,500 m³, and the capacity of the sedimentation tank was 800 m³.

The bioreactor had an anaerobic treatment tank of 80 m³ capacity, and ananaerobic treatment tank of 250 m³ capacity. The treated water wascirculated within the bioreactor at a circulation rate in the range of3-6.

Sludge produced in the sedimentation tank was added continuously by ametering pump to the interior of the waste water aeration-conditioningtank. The added amount was supplied at a rate such that the sludgeconcentration within the waste water aeration-conditioning tank,expressed as MLSS, was in the range of 1,500-2,000 mg/L. The amount ofaeration was adjusted to regulate the ORP to +50 mV.

The treated waste water having undergone aeration-conditioning in thewaste water aeration-conditioning tank to bring the ORP to a positivevalue was supplied to a KF800 non-dosing type pressurized flotationconcentration-separation tank (made by Japan ALSI Co. Ltd.). In thispressurized flotation concentration-separation tank, a mixture of 100weight parts of 5 Kg/cm² pressurized water per 100 weight parts oftreated waste water was circulated, without chemical dosing.

The sludge separated by the pressurized flotationconcentration-separation tank underwent return treatment to thebioreactor. In the bioreactor, in the anaerobic treatment tank, the pHwas 7.1, the ORP was −350 mV, and the DO was 0; in the aerobic treatmenttank, the pH was 6.1, the ORP was +210 mV, and the DO was 0.8 mg/L.

The excess sludge produced in the bioreactor was supplied to the diluteactivated sludge aeration tank. The release water from the bioreactorwas supplied to a full-capacity dilute activated sludge aeration tank.

The treated waste water obtained from the pressurized flotationconcentration-separation tank was sent to the dilute activated sludgeaeration tank and treated. The dilute activated sludge aeration tank wassupplied with the excess sludge produced in the bioreactor. In thedilute activated sludge aeration tank, the excess sludge was acclimatedto activated sludge suitable for treated waste water.

The treated waste water treated in the dilute activated sludge aerationtank was released after passing through the sedimentation tank. Thesludge sedimented in the sedimentation tank was recirculated to thewaste water aeration-conditioning tank. Through these sludge circulationsteps, reductions in the amount of sludge were achieved.

The water quality of the release water was a BOD of 8 mg/L, a COD of 10mg/L, a T-N of 0 mg/L, an n-Hex of 0 mg/L, and an SS of 1 mg/L.

Production of dewatered cake was 0-20 tons/month.

During waste water treatment by the above described method, becauseanaerobic-aerobic operation can take place while minimizing theproduction of toxic gases in the bioreactor, the autodigestioncapability of the microbes is improved. Moreover, in the course ofcirculation of the sludge, microbes capable of selectively decomposingcontaminant substances in the waste water become acclimated, so thatpersistent contaminant substances can be readily treated. As a result,effects such as (1) dramatic reductions in the discharged amount ofdewatered cake, (2) elimination of foul odors in proximity to thepressurized flotation concentration-separation tank, and the like wereobserved.

Example 2

Wastewater discharged from a confection production facility was treated.

Prior to treatment, the waste water had a BOD of 6,000 mg/L, a COD 3,500mg/L, a T-N of 120 mg/L, an n-Hex of 3,000 mg/L, and an SS of 350 mg/L,the amount of treated water being 120 m³/day. At this facility, afteradding an inorganic flocculant such as polyaluminum chloride to thepressurized flotation tank to bring about flocculation andsedimentation, conventional waste water treatment was conducted by themethod shown in FIG. 4. For this reason, dewatered cake (water content85 wt %) was produced as a rate of 150 tons/month.

The sludge collection tank and dewatering device shown in FIG. 4 wereremoved, and in a portion of the removal site was installed a bioreactorshown in FIG. 2, having an anaerobic treatment tank of 100 m³ capacity,and an aerobic treatment tank of 250 m³ capacity. The treated wastewater was circulated within the bioreactor at a circulation rate in therange of 5-8.

An aeration device was attached to the conventional waste waterconditioning tank shown in FIG. 4, to convert it to a waste wateraeration-conditioning tank. The conventional aeration tank, redeployedas a dilute activated sludge aeration tank, and the sedimentation tank,redeployed as a sedimentation tank, were respectively attached to thesludge circulation pathway shown in FIG. 1.

At this facility, the capacity of the waste water aeration-conditioningtank was 100 m³, the capacity of the pressurized flotationconcentration-separation tank was 10 m³, the capacity of the diluteactivated sludge aeration tank was 120 m³, and the capacity of thesedimentation tank was 30 m³.

The sludge produced in the sedimentation tank was continuously addedinto the waste water aeration-conditioning tank by a metering pump. Theadded amount was supplied at a rate such that the sludge concentrationwithin the waste water aeration-conditioning tank, expressed as MLSS,was in the range of 3,500-5,000 mg/L. The amount of aeration wasadjusted to regulate the ORP to +100 mV.

The treated waste water having undergone aeration-conditioning in thewaste water aeration-conditioning tank to bring the ORP to a positivevalue was supplied to a KF800 non-dosing type pressurized flotationconcentration-separation tank (made by Japan ALSI Co. Ltd.). In thispressurized flotation concentration-separation tank, a mixture of 220weight parts of 4.5 Kg/cm² pressurized water per 100 weight parts oftreated waste water was circulated, without chemical dosing.

The sludge separated by the pressurized flotationconcentration-separation tank underwent return treatment to thebioreactor. In the bioreactor, in the anaerobic treatment tank, the pHwas 7.4, the ORP was −400 mV, and the DO was 0; in the aerobic treatmenttank, the pH was 7.8, the ORP was +210 mV, and the DO was 1.8 mg/L.

The excess sludge and release water produced in the bioreactor wassupplied to the dilute activated sludge aeration tank.

The treated waste water obtained from the pressurized flotationconcentration-separation tank was sent to the dilute activated sludgeaeration tank and treated in the same manner as in Example 1, thetreated water being released after passing through the sedimentationtank. The sludge sedimented in the sedimentation tank was recirculatedto the waste water aeration-conditioning tank.

The water quality of the release water was a BOD of 18 mg/L, a COD of 30mg/L, a T-N of 1 mg/L, an n-Hex of 1 mg/L, and an SS of 30 mg/L.

Production of dewatered cake was 0 tons/month.

In the confection production facility as well, effects such as (1)dramatic reductions in the discharged amount of dewatered cake, (2)elimination of foul odors in proximity to the pressurized flotationconcentration-separation tank, and the like were observed.

INDUSTRIAL APPLICABILITY

The method of the present invention discharges substantially no excesssludge, thereby affording an environmentally-friendly wastewatertreatment method having minimal environmental impact; and moreoverrequires no equipment for dewatered cake treatment, and therefore can beutilized going forward as a method to upgrade numerous existing wastewater treatment equipment. In particular, facilities located in urbanareas typically require odor abatement equipment to deal with copiousfoul odors produced by waste water conditioning tanks, pretreatmentequipment, and dewatering treatment equipment. However, by introducingthe present treatment method, no foul odors are produced in thetreatment steps leading from the waste water conditioning tank for wastewater treatment, to final treatment. For this reason, the presenttreatment method represents a treatment method suited to abatement offoul odors by minimizing the production of foul odors associated withtreatment, in some cases rendering odor abatement equipment unnecessary.

EXPLANATION OF REFERENCE SYMBOLS AND NUMERALS

-   1 Bioreactor-   2 Outer tank-   3 Cylindrical inner tank-   4 Circulation rate control device-   5 Cylindrical control plate-   6 Treated water quality measurement device-   7 Rotating shaft-   8 Air injection port-   9 Support post-   10 Waste water supply port-   11 Treated water release port-   12 Sedimentation-solidification prevention device-   13 Sludge extraction port

The invention claimed is:
 1. An activated sludge treatment method fortreatment of wastewater by a circulation system equipped with a wastewater aeration-conditioning tank, a pressurized flotationconcentration-separation tank, a dilute activated sludge aeration tank,a bioreactor, and a sedimentation tank, sludge being circulated amongthe tanks, wherein the activated sludge treatment method ischaracterized by comprising: a step 1 in which sludge 2 produced in thesedimentation tank is supplied to the waste water aeration-conditioningtank supplied with waste water prior to treatment; a step 2 in whichwaste water into which the sludge 2 has been mixed is subjected toaeration-conditioning in the waste water aeration-conditioning tank, tobring the oxidation-reduction potential to a positive value, and theconditioned waste water is then supplied to the pressurized flotationconcentration-separation tank; a step 3 in which the sludge 1 producedthrough treatment in the pressurized flotation concentration-separationtank is supplied to the bioreactor; a step 4 in which the treated wastewater 1 separated from the pressurized flotationconcentration-separation tank is supplied to the dilute activated sludgeaeration tank; a step 5 in which released water and the sludge 3produced by treatment in the bioreactor are supplied to the diluteactivated sludge aeration tank; and a step 6 in which the treated wastewater 2 separated from the dilute activated sludge aeration tank issupplied to the sedimentation tank wherein the bioreactor is equippedwith an outer tank; a cylindrical inner tank situated in the interior ofthe outer tank and having openings at top and bottom; a circulation ratecontrol device provided in an upper part of the cylindrical inner tank,and adapted for controlling the rate of circulation of treated waterinside the tank; a cylindrical control plate provided to the outsideperimeter in an upper part of the cylindrical inner tank, and adaptedfor inducing sedimentation of the sludge; treated water qualitymeasurement devices provided outside and inside the cylindrical innertank; a waste water supply port provided to a circulation pathway of thetreated water circulated within the outer tank and the inner tank; and atreated water release port provided to an upper part of the outer tank;the cylindrical inner tank being divided, by a partitioning wall havinga passage hole in a center part, into a cylindrical top part and acylindrical bottom part, the cylindrical top part constituting anaerobic microorganism treatment tank having a conical trapezoidal apicalpart open at the top face and the bottom face and provided with aplurality of air injection ports in a peripheral edge part of thepartitioning wall and surrounding the passage hole within thecylindrical top part, and the cylindrical bottom part constituting ananaerobic microorganism treatment tank having an open part at the bottomface; the bioreactor being provided with stirring devices for stirringthe aerobic microorganism treatment tank and the anaerobic microorganismtreatment tank; and provided with means for detecting at least onemeasured value selected from the hydrogen ion concentration, theoxidation-reduction potential, and the dissolved oxygen content of thetreated water measured by the treated water quality measurement devices,and with means provided to the circulation rate control device accordingto the detected measured value, and adapted for controlling the rate atwhich water circulates within the tank to 3-20, through control of atleast one quantity selected from opening-closing of a fluid leveladjustment valve, vertical movement of a fluid level adjustment controlpanel, and the quantity of air blown in from the air injection ports;wherein anaerobic microorganism treatment and aerobic microorganismtreatment take place in successive fashion through circulation ofactivated sludge, together with waste water supplied from the wastewater supply port, within the tank, through the interior of thecylindrical inner tank, the outside peripheral face of the cylindricalinner tank, and within activated sludge that has sedimented to a bottompart of the outer tank.
 2. The activated sludge treatment methodaccording to claim 1, characterized in that the sludge 2 supplied to thewaste water aeration-conditioning tank is supplied in a range such thatthe sludge concentration within the waste water aeration-conditioningtank, expressed as the mixed liquor suspended solids is 500-8,000 mg/L.3. A method for upgrading existing waste water treatment equipment toreduce the amount of sludge produced by waste water treatment equipment,to a lower level than the amount of sludge produced by the existingwaste water treatment equipment, wherein the method for upgradingexisting waste water treatment equipment is characterized by comprising:a step in which the bioreactor according to claim 1 is newly equippedwith both an existing or upgraded pressurized flotationconcentration-separation tank and an existing or upgraded diluteactivated sludge aeration tank to form a newly equipped bioreactor; anda circulation step in which sludge is circulated via the newly equippedbioreactor.